#Smokefree: testing a school-based active involvement intervention to reduce smoking among adolescents.

Approved 24/05/2023, Social and Societal Ethics Committee (SMEC) (Dekenstraat 2 - box 3700, Leuven, 3000, Belgium; +32 (0)16 32 71 39; smec@kuleuven.be), ref: G-2020-2267-R6(AMD)

The following measures will be assessed in the baseline, posttest and delayed posttest questionnaire. The scales will be used for smoking/vaping separately.
1. Attitudes toward smoking/ vaping assessed using six 7-point semantic differential items (based on Mesman et al., 2020)
2. Injunctive norms toward smoking/vaping assessed using a 7-point Likert scale, indicating participants’ agreement with three statements regarding the perceived approval of important others related to smoking behaviors (based on Mesman et al., 2020)
3. Descriptive norms toward smoking/vaping assessed using a slider ranging from 0% to 100% to assess the perceived number of peers engaging in these behaviors (based on Greene et al., 2021)
4. Positive outcome expectations toward smoking and vaping assessed using a 7-point Likert scale, indicating agreement with 7 statements regarding the positive consequences of smoking (Based on Barker et al., 2019; Dalton et al., 1999)
5. Negative outcome expectations toward smoking/vaping assessed using a 7-point Likert scale, indicating agreement with five statements regarding the negative consequences of smoking (Barker et al., 2019, Dalton et al, 1999)
6. Willingness to smoke/vape assessed using a 7-point Likert scale, indicating agreement with four statements that assert the willingness to take/decline cigarettes based on a fictitious scenario (based on Gerrard et al., 2005; Vogel et al., 2021)
7. Intention to smoke/vape assessed using a 7-point Likert scale, indicating agreement with three statements that assess the intention to engage in smoking (adapted from Mesman et al., 2020)

The secondary outcome measures consist of smoking/vaping frequency and quantity questions, as well as some media literacy questions. Furthermore, some other components related to the intervention will be assessed.

Smoking/vaping frequency and quantity at immediate post-test measurement:
1. In the immediate posttest survey, participants will be asked whether they have engaged in smoking/vaping during the last month.
2. In the immediate posttest survey, participants who have engaged in smoking/vaping will be asked how often they engaged in this behavior (based on Rosiers et al., 2023).
3. In the immediate posttest survey, participants who have engaged in smoking/vaping will be asked how many cigarettes/vapes they have smoked.
4. Participants will be asked how likely it would be that they would quit smoking/vaping in the next 6 months using a 7-point semantic differential scale (self-developed).

Smoking/vaping frequency and quantity at delayed post-test measurement:
1. In the delayed post-test survey, participants will be asked whether they have engaged in smoking/vaping during the last 6 months
2. In the delayed post-test survey, participants who have engaged in smoking/vaping will be asked how often they engaged in this behavior (based on Rosiers et al., 2023)
3. In the delayed posttest survey, participants who have engaged in smoking/vaping will be asked how many cigarettes/vapes they have smoked
4. Participants will be asked how likely it would be that they would quit smoking/vaping in the next 6 months using a 7-point semantic differential scale (self-developed)

Media literacy components at baseline, immediate post-test and delayed post-test:
1. Critical thinking about source and message assessed using a 7-point Likert scale with 6 statements (Based on Austin et al., 2015)
2. Reflective thinking about the role of media assessed using a 7-point Likert scale with 4 statements (based on Pinkleton et al., 2007)
3. Perceived similarity assessed using a 7-point Likert scale with 5 items (based on Pinkleton et al., 2007)
4. Perceived realism assessed using a 7-point Likert scale with 4 items (based on Pinkleton et al., 2007)
5. Perceived desirability assessed using a 7-point Likert scale with 6 items (based on Pinkleton et al., 2007)
6. Wishful identification assessed using a 7-point Likert scale with 3 items (based on Pinkleton et al., 2007)
7. Skepticism about the media assessed using a 7-point Likert scale with 6 items (based on Pinkleton et al., 2007)
8. Self-efficacy to influence others assessed using a 7-point Likert scale with 3 items (based on Pinkleton et al. 2017)
9. Inform others about the risks of media assessed using a 7-point Likert scale with 4 items (Based on Pinkleton et al., 2017)

At immediate posttest, participants in the intervention condition will also be assessed:
1. Engagement assessed using a 7-point Likert scale with 9 items (Based on Greene et al., 2015)